The invention concerns a steering device with a steering angle transducer, a steering drive having a motor and a first gear, at least one wheel driven by the steering drive and a sensor arrangement for detecting the angle position of the wheel with a detection device, which produces a reference signal for at least one reference position of the steering device.
A steering device of this kind is known from DE 197 14 786 C1.
Such steering devices are, for example, used in forklift trucks, used in warehouses for transporting palleted goods. Usually, they have a three-wheel configuration, the rear wheel being steered. However it is also possible for such a vehicle to have four wheels, two wheels being steered in pairs or all wheels being steered. For reasons of clarity, however, it will be assumed in the following that only one wheel is steered.
In the known steering device, the sensor arrangement has a sensor, which detects the relative rotation of the motor shaft. With relatively small efforts, such detection can be made with the required accuracy. To make sure that this relative movement is related to a fixed starting position, a detection device is provided, which produces a reference signal at a reference position of the steering drive. This detection device has a trigger on a transmission element of the steering drive, which cooperates with a detector. The trigger is arranged on a chain, which connects a gear wheel on the driven wheel with a gear wheel on the output shaft of the gear.
In most cases, this steering device works satisfactorily. Problems occur, when the vehicle is used in a heavily contaminated environment, for example, a foundry or a waste utilisation plant. In these cases, there is a risk that the detection device is contaminated, thus not being able to work accurately any longer. Additionally, there is a risk that the detection device is damaged.
The invention is based on the task of increasing the reliability of the steering device.
In a steering device as described in the introduction, this task is solved in that the detection device is connected with the motor via a second gear.
Thus, selecting the placing or positioning of the detection device is free. It is no longer required to arrange the detection device close to the steered wheel. On the contrary, via the second gear it can be arranged in a position, in which less contamination or a reduced risk of damaging is anticipated. By means of the second gear, it is possible to produce the reference signal of the reference position, that is, the advantages obtained until now are maintained to the full extent.
In this connection, it is particularly preferred that the gear ratio of the second gear is so high that its output shaft connected with the detection device performs not more than one complete rotation, when the driven wheel moves from one extreme position to the other. Thus, exactly one angle position of the output shaft of the drive is allocated to each angle position of the driven wheel, so that the reference signal can only be produced at the reference position. Actually, then the detection device would be sufficient to determine the angle position of the steered wheel. However, then extremely accurately working detection devices would be required, which can be avoided, if, for example, as shown in DE 197 14 786 C1, additional sensors are used.
Preferably, the second gear has the same gear ratio as the product of all gear ratios between the output shaft of the motor and the driven wheel. This results in a 1:1 ratio between the output shaft of the second gear, on which the detection device for detecting the reference position is arranged, and the steered wheel. An embodiment of this kind is particularly advantageous, when the steered wheel has no mechanical stops, but can be turned more or less optionally several times. Also in this case, a reference position can always be xe2x80x9cfoundxe2x80x9d, on the basis of which the change of the rotation angle can be detected.
Preferably, the second gear and the detection device are integrated in the steering drive. For example, this means that the second gear and the detection device are also covered by a housing arranged on the steering drive. This reduces the risk of contamination and the risk of damaging. Additionally, the complete steering device becomes compact and easier to mount.
Preferably, the detection device is made as a touchfree working detection device. This reduces wear, and on a long sight thus ensures an accurate detection of the reference position.
In a particularly preferred embodiment, it is provided that the detection device performs no reaction forces on the outlet shaft of the second gear. Accordingly, the gear can be made very cheap. It is not supposed to transmit forces. Merely the internal friction of the gear must be overcome. Such gears can, for example, be made of a plastic material, so that their weight remains small. As the gear does not contain any load transmitting function, it can also be made relatively cheap.
Advantageously, the sensor arrangement has a sensor, which detects a relative movement of the motor shaft, the sensor producing more than one pulse per rotation. A sensor, which detects a relative movement of the motor shaft, is known from the DE 197 14 786 C1 mentioned above. As a matter of fact, this sensor can, in a manner of speaking, incrementally determine the number of rotations performed by the motor shaft. As the gear ratio between the motor shaft and the driven or steered wheel is known, the number of rotations of the motor shaft will permit a conclusion with regard to the deflection of the steered wheel. When now per rotation of the motor shaft, which may also already be geared by a gear with constant ratio, more than one pulse is produced, the evaluation can be made far more accurate.
In this connection, it is particularly preferred that the number of pulses per rotation is an exponent of the number 2. That is, for example, 16, 32, 64 or 128 pulses per rotation. The higher the number of pulses is, the better and more exact is the resolution.
Preferably, the detection device and the sensor are connected with a control device, which has a counter, counting the pulses of rotations in one direction positively and of rotations in the other direction negatively, a control device being provided, which produces an error signal, if the counter exceeds zero by a predetermined amount, when the detection device displays the passing of the reference position. Counting up and down is a relatively simple measure of determining the steering angle of the driven wheel. Due to mechanical insufficiencies, however, a difference between the actually counted pulses and the steering angle of the wheel will occur in many cases. To compensate for this error, the reference position is provided. Normally, the counter will be reset to zero when reaching the reference position, so that the subsequent steering movements can again be detected with the desired reliability. However, if on reaching the reference position, it turns out that the error is too large, that is, exceeds a predetermined tolerance, an error message will be produced to warn the driver of the vehicle or to effect a test and maintenance of the steering device.
Advantageously, a section of the output shaft of the motor, on which the sensor is arranged, traverses the second gear. Thus, the sensor and the detection devices are also physically arranged next to each other. This gives several advantages. Firstly, space is saved. Both units can be held in one housing. Both arrangements are submitted to the same environmental conditions. Secondly, the risk of different measuring results caused by a difference in location is relatively small.